1. Field of the Invention
The present invention relates to a clamping device for retaining a workpiece when conveying the workpiece needed to be positioned with a high precision and a workpiece conveying robot including the clamping device.
2. Description of the Related Art
Conventionally, in order to convey workpieces such as semiconductor wafers or glass substrates, there is used a workpiece conveying robot for retaining and conveying these workpieces on a hand portion.
In the case of applying precision processing to such workpieces, a workpiece conveying robot is needed to deliver these workpieces to a device in a next step with a high positional precision. Thus, the workpiece conveying robot is required to retain and convey the workpieces placed on the hand portion while performing positioning on the hand portion with a high precision and then deliver the workpieces while maintaining a position precision of the workpieces.
In order to cause the hand portion to have the function as described above, a clamping device for precisely retaining a workpiece is provided at the hand portion. As this clamping device, for example, there exists a substrate retaining device described in Granted Japanese Patent No. 4600856. This device is configured in such a manner that stationary clamps are respectively provided in a pair at a distal end side and a proximal end side of the hand portion (a hand), and a movable clamp is provided between the fixing clamps on the proximal end side. In addition, at these stationary clamps and the movable clamp, upward tilt faces tilting downwardly toward a central direction of all of the workpieces (wafers) are formed. Further, after the workpieces have been placed on the stationary clamps, the movable clamp is moved from the outside of the workpieces toward the central direction, whereby retention of the workpieces are performed while alignment of the workpieces are precisely performed by means of the stationary clamp on the distal end side and the movable clamp.
However, the clamping device (a substrate retaining device) described in Granted Japanese Patent No. 4600856 performs positioning by means of the stationary clamp on the distal end side and the movable clamp on the proximal end side when retaining a workpiece and thus there is an apprehension that the workpiece is spaced from the stationary clamp on the proximal end side. Therefore, when the movable clamp is retracted to thereafter release retention of the workpiece, a current state changes from a state in which the proximal end side of the workpiece is supported by means of the movable clamp to a state in which it is supported by means of the stationary clamp and thus a position of the workpiece may be shifted accordingly.
Herein, in order to specifically clarify the problem described above, a conventional clamping device 901 having a configuration which is similar to that of Granted Japanese Patent No. 4600856 is schematically shown in FIG. 11 and FIG. 12.
In this clamping device 901, stationary blocks (equivalent to stationary clamps) 941, 951 are respectively provided in a pair on a side of a distal end 31b and on a side of a proximal end 31a of a workpiece retaining base 31 (these blocks are shown for short on one-by-one basis in the figures), and in these stationary blocks 941, 951, upward tilt faces 941a, 951a, which tilt downwardly toward a center of a workpiece W, are respectively provided. In addition, in the stationary block 941 on the side of the distal end 31b, a protrusion portion 941b that is continuous to the upward tilt face 941a and extends upwardly is formed, and a side face 941c inside of the protrusion portion is capable of abutting against a side face of the workpiece W.
Further, a movable block (equivalent to a movable clamp) 961 is provided between a pair of stationary blocks 951 that are provided on the side of the proximal end 31a, and at a distal end of the movable block, an upward tilt face 961a tilting downwardly toward the center of the workpiece W is formed. Furthermore, a vertical face 961c that is continuous to the tilt face 961a and extends upwardly may also be formed.
When the workpiece W is retained by employing the thus configured clamping device, first, as shown in FIG. 11 (a), the workpiece W is placed so that an edge on a lower side forming a side face of the workpiece W, specifically a part of this side face, abuts against the upward tilt faces 941a, 951a of the respective stationary blocks 941, 951. Further, as shown in FIG. 11 (b) to FIG. 11 (c), by moving the movable block 961 in the central direction of the workpiece W, the workpiece W is moved and subsequently while a side face of the workpiece is adapted to abut against the side face 941c of the stationary block 941, positioning is performed and at the same time the workpiece W is retained.
At this juncture, an edge on an opposite side, that is, on the left side in the figure, is supported by means of the upward tilt face 961a or the vertical face 961e of the movable block 961 and then is spaced by the upward tilt face 951a of the stationary block 951 on the side of the proximal end 31a. 
The workpiece W is conveyed while it is thus retained, and thereafter, in the case where release of retention is performed at a predetermined position, as shown in FIG. 12 (d) to FIG. 12 (e), the movable block 961 is operated and retracted in an opposite direction to that of the workpiece W. At this juncture, the workpiece W loses the supporting exerted by the upward tilt face 961a of the movable block 961 and then this workpiece is supported again by means of the upward tilt face 951a of the stationary block 951 on the side of the proximal end 31a. At this time, the position of the workpiece W may be shifted in proportion to a distance spaced when the workpiece W is retained, and as shown in the figure, a case in which the workpiece W tilts or a case in which the workpiece is entirely positionally shifted downwardly is also presupposed.
In addition, as is understood from FIG. 11 (c), in this configuration, an upper side is released with the workpiece W being supported from a lateral side or a lower side when the workpiece is retained and thus if a vibration in a vertical direction occurs, the workpiece W may also be shifted upwardly to thereafter disable retention. That is, a force of retention of the workpiece W relative to a vibration can be said to be small.
It is an object of the present invention to effectively solve the problem as described above, and specifically, it is an object of the present invention to provide a clamping device for retaining a workpiece with a high positional precision, enabling release of retention while maintaining the position precision, and further, having a strong force of retention relative to a vibration, and a workpiece conveying robot including the clamping device.